Whirlpools: Extreme Eddies or Magnificent Maelstroms?
Everyone knows what a whirlpool is. Romanticised in popular literature for thousands of years by the likes of Edgar Allen Poe and Jules Verne, by Melville and Homer– ever since Odysseus snuck past Charybdis in the epics of Ancient Greece- whirlpools have struck equal measures of terror and awe into the hearts of mariners. But what do we really know about real-life, currently-existing whirlpools? Are they the ship-crushing maws of the ocean? Or are they in actual fact, benign eddies, a safe haven not for monsters, but for all manner of marine life?
Location: Off the Edge of the Map
It is easy to see why whirlpools have been a source of inspiration for so long. Beyond their destructive capabilities, notable whirlpools are often in remote places with names seemingly designed to fire the imagination.
Two of the most notable whirlpools in the world are located in Norway and are remarkable for different reasons. Saltstraumen is the name of the connecting channel between two fjords-Saltfjorden and Skjerstadfjorden– where water speeds have been recorded up to 41km/hour, making it the strongest current of any strait in the world. Moskstraumen located between Lofoton Point and Mosken Island also off the coast of Norway is remarkable in that it forms offshore; unlike most other whirlpools which form in narrow straits. This whirlpool was first described in the 13th century, was mapped by a Olaus Magnus on the Carta Marina in 1539 and was the inspiration of “Descent into the Maelstrom” written by Edgar Allen Poe in 1841; thus demonstrating that whirlpools are not ephemeral reactions but permanent oceanographic features.
Other prominent whirlpools include the Naruto Pools found in a strait between the Tokushima city of Naruto and the Awaji Island in Japan, the Gulf of Corryvreckan between the Scottish islands of Scarba and Jura and Old Sow whirlpool between Deer Island in Canada and Moose Island in Maine.
Formation: In the Straight and Narrow
Whirlpools are a result of both tidal factors and topographical factors. Saltfjorden is entirely open to the sea but Skjerstadfjorden is almost entirely sealed by land- apart from a strait less than 500m through which 400 million cubic metres of water passes every day thus creating Saltstraumen. On the falling tide water drains out of Skjerstadfjorden and passes through Saltstraumen at a rate of 4 metres per second creating cyclonic and anti-cyclonic vortices either side of Saltstraumen. However on the rising tide the vortices almost vanish and for a short period Saltstraumen is safe enough for shipping to pass through the strait.
In Scottish mythology the whirlpool in the Gulf of Corryvreckan was created by a hag goddess of winter who washed her great plaid in the gulf ushering in the change of seasons. In reality the daily tide flooding out of the Firth of Lorne meet a 41m tall underwater pinnacle of basalt which protrudes to just 30m below the surface and a deep hole in the seabed topography. When fast moving water, for example on spring tides, meets these obstructions complex currents and eddies are formed, water is pushed upwards and sometimes spirals around the pinnacle to create a whirlpool. Even when the whirlpool does not form, waves up to 9m in height are common.
Moskstraumen- origin of the word maelstrom which has come to be synonymous with whirlpool- is formed in a different way. The semi-diurnal tides rise 4m in the Lofoton Islands and when combined with the northerly sea currents and strong local winds currents passing between Lofoton Point and Mosken Island can reach up to more than 11km hour even at a depth of 500m. Between the two landmasses and part of a local island chain lies a submarine ridge which rises to just 60m below sea level. When the deep fast currents meet this ridge, water is forced upwards creating a whirlpool 50m in diameter with waves of 1m in amplitude.
Devastation: The Teeth in the Mouth of the Ocean
Obviously attempting to navigate such extreme currents carries risks. In 1947 author George Orwell had to be rescued from drowning in the Gulf of Corryvreckan after a mistimed trip. However the only other incident in the Gulf was when a Norwegian barque was blown from anchor nearby in a storm and again all the crew survived. In fact despite their fearsome reputation it seems like whirlpools have gained, or maybe always had, a bad reputation from popular media. Homer was smashing ships in Charybdis in 500 BC! Yet shipping passes through Saltstraumen daily and it is actually a major tourist attraction for the region where it is possible to go on ferry trips, hire boats and even fish, close up to the whirlpool.
Habitation: Here be Krakens
A recent study has found that the Gulf of Corryvreckan is an attractive environment to Phoecoena phocoena (harbour porpoises). P. phoecoena track the movement of the whirlpool over time and tend to move downstream in the direction of tidal flow. The reason for their attraction to such a high energy site is undoubtedly elevated availability of food. There are several features of whirlpools which make them attractive foraging grounds: turbulence, three-dimensional flow structure and upwelling all mean that phyto and zoo-plankton are caught in these environments and brought to the surface making them easy pickings for fish which in turn draw seabirds, P. phocoena and other megafauna such as seals. Human are another top predator attracted to whirlpools. The world record for the largest Pollock caught on a line and pole was set at Saltstraumen.
So in conclusion it seems that whirlpools do not deserve the dire reputation with which they have been burdened, life does thrive here, however it cannot be denied that these high energy environments, are one extreme marine habitat.